Objective
The standard-model of the electroweak and the strong interaction is extremely successful in describing a large number of experimental data. Nevertheless it seems obvious to most of the scientists involved that the standard-model with its group structure SU(2) x U(1) x SU(3) is not the final answer. As a next step it is hoped to unify the electroweak interaction of Glashow, Salam and Weinberg with quantum chromodynamics (QCD). The preferred grand unified theories are at the moment left-right symmetric models, which predict that the neutrino is a Majorana particle and therefore identical apart from phase with its antiparticle. Such left-right symmetric theories allow also for a right-handed weak interaction, which is reduced relative to the left-handed weak interaction by a much larger mass of the vector bosons, which mediate the right-handed weak interaction. In this model one has six different neutrinos which all have a finite mass. The model allows for processes which are forbidden in the standard-model. One process allowed is the neutrinoless double-beta decay which will be studied in this project. The present experimental lower limits on the life times against the neutrinoless double-beta decay allow upper limits to be given for averaged neutrino masses, an averaged mixing angle for the vector bosons mediating left and mediating right-handed weak interactions and lower limits for the heavy vector boson mediating mostly right-handed weak interactions suitably multiplied by linear combinations of the coefficient of the unitary matrix transforming the weak eigenstates of the neutrinos into the mass eigenstates.
The main problem in the theoretical calculations, which are investigated in this project, are the nuclear structure calculations of the relevant matrix elements. The project will include proton-neutron pairing and particle number projection to describe more reliably the excited states of the intermediate nucleus. The same nuclear structure, which is important in order to calculate the interesting zero neutrino double-beta decay, is also involved if one wants to calculate the two neutrino double-beta decay where the project will have experimental measurements and the double charge exchange reaction on nuclei. The same nuclear many-body problem will also be solved for lepton number violating reactions like (myon electron) on nuclei.
Although almost all scientists involved believe that QCD is the theory of the strong interaction, until now it has been impossible to calculate such a simple thing as the structure of the pion or the proton. One needs models at low energies (or pure numerical approaches: lattice QCD) to find reasonable descriptions of low energy hadronic processes. The project will investigate quark degrees of freedom in hadrons and nuclei using quark models. Especially the dibaryon resonances will be studied. An experimental group from Tübingen and Karlsruhe recently claimed that they found such a dibaryonic resonance at around 2 GeV. In addition the project will show that one should be able to see experimentally quark degrees of freedom in the deuteron and in light nuclei.
Topic(s)
Call for proposal
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72076 Tübingen
Germany